Polyester bottle resins having reduced frictional properties and methods for making the same

ABSTRACT

The invention is a polyester resin that includes between about 20 and 200 ppm of an inert particulate additive, preferably selected from the group consisting of surface-modified talc and surface-modified calcium carbonate. The invention is also a method of making the polyester resin, which is capable of being formed into low-haze, high-clarity bottles possessing reduced coefficient of friction.

CROSS-REFERENCE TO RELATED APPLICATION

This application incorporates entirely by reference co-pending andcommonly-assigned application Ser. No. 09/738,150, for Methods ofPost-Polymerization Injection in Continuous Polyethylene TerephthalateProduction.

FIELD OF THE INVENTION

The invention relates to a polyester resin that includes small amountsof an inert particulate additive, which reduces the coefficient offriction in bottles formed from the polyester resin while maintainingbottle clarity.

BACKGROUND OF THE INVENTION

Polyester resins, especially polyethylene terephthalate (PET) and itscopolyesters, are widely used to produce rigid packaging, such astwo-liter soft drink containers. Polyester packages produced bystretch-blow molding possess high strength and shatter resistance, andhave excellent gas barrier and organoleptic properties as well.Consequently, such plastics have virtually replaced glass in packagingnumerous consumer products (e.g., carbonated soft drinks, fruit juices,and peanut butter).

In conventional techniques of making bottle resin, modified polyethyleneterephthalate is polymerized in the melt phase to an intrinsic viscosityof about 0.6 deciliters per gram (dl/g), whereupon it is polymerized inthe solid phase to achieve an intrinsic viscosity that better promotesbottle formation. Before 1965, the only feasible method of producingpolyethylene terephthalate polyester was to use dimethyl terephthalate(DMT). In this technique, dimethyl terephthalate and ethylene glycol arereacted in a catalyzed ester interchange reaction to formbis(2-hydroxyethyl)terephthalate monomers and oligomers, as well as amethanol byproduct that is continuously removed. Thesebis(2-hydroxyethyl)terephthalate monomers and oligomers are thencatalytically polymerized via polycondensation to produce polyethyleneterephthalate polymers.

Purer forms of terephthalic acid (TA) are now increasingly available.Consequently, terephthalic acid has become an acceptable, if notpreferred, alternative to dimethyl terephthalate as a starting materialfor the production of polyethylene terephthalate. In this alternativetechnique, terephthalic acid and ethylene glycol react in a generallyuncatalyzed esterification reaction to yield low molecular weightmonomers and oligomers, as well as a water byproduct that iscontinuously removed. As with the dimethyl terephthalate technique, themonomers and oligomers are subsequently catalytically polymerized bypolycondensation to form polyethylene terephthalate polyester. Theresulting polyethylene terephthalate polymer is substantially identicalto the polyethylene terephthalate polymer resulting from dimethylterephthalate, albeit with some end group differences.

Polyethylene terephthalate polyester may be produced in a batch process,where the product of the ester interchange or esterification reaction isformed in one vessel and then transferred to a second vessel forpolymerization. Generally, the second vessel is agitated and thepolymerization reaction is continued until the power used by theagitator reaches a level indicating that the polyester melt has achievedthe desired intrinsic viscosity and, thus, the desired molecular weight.More commercially practicable, however, is to carry out theesterification or ester interchange reactions, and then thepolymerization reaction as a continuous process. The continuousproduction of polyethylene terephthalate results in greater throughput,and so is more typical in large-scale manufacturing facilities.

When the polymerization process is complete, the resulting polymer meltis typically extruded and pelletized for convenient storage andtransportation. Thereafter, the polyethylene terephthalate may be moldedinto preforms and bottles.

As will be understood by those having ordinary skill in the art,polyethylene terephthalate is typically converted into a container via atwo-step process. First, an amorphous bottle preform is produced frombottle resin by melting the resin in an extruder and injection moldingthe molten polyester into a preform. Such a preform usually has anoutside surface area that is at least an order of magnitude smaller thanthe outside surface of the final container. The preform is reheated toan orientation temperature that is typically 30° C. above the glasstransition temperature. The reheated preform is then placed into abottle mold and, by stretching and inflating with high-pressure air,formed into a bottle. Those of ordinary skill in the art will understandthat any defect in the preform is typically transferred to the bottle.Accordingly, the quality of the bottle resin used to forminjection-molded preforms is critical to achieving commerciallyacceptable bottles.

Polyethylene terephthalate bottles, especially straight-walled two-litersoft drink bottles, often possess high coefficients of friction (COF).This is a significant problem in the bottling industry as excessivefriction between adjacent bottles prevents such bottles from easily andefficiently sliding past one another as they are depalletized. Toimprove depalletizing, bottlers conventionally resort to water mistingand line lubrication on a filling line.

Therefore, there is a need for a polyester bottle that possesses reducedcoefficient of friction while retaining bottle clarity.

OBJECT AND SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide ahigh-clarity polyester bottle including a surface-modified talc orsurface-modified calcium carbonate in concentrations that permit thebottle to possess reduced coefficient of friction.

It is a further object of the present invention to provide a method formaking polyethylene terephthalate preforms and bottles possessingreduced coefficients of friction.

It is a further object of the present invention to provide a polyesterresin that is capable of being formed into high-clarity bottlespossessing reduced coefficient of friction.

It is a further object of the present invention to provide a method formaking polyethylene terephthalate resin that can be formed intohigh-clarity bottles possessing reduced coefficient of friction.

The foregoing, as well as other objectives and advantages of theinvention and the manner in which the same are accomplished, is furtherspecified within the following detailed description and its accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the qualitative effect on bottle sidewall haze andfriction as a function of increasing concentration of the reduced COFadditive.

FIGS. 2 and 3 illustrate the theoretical loss of intrinsic viscosity ofpolyethylene terephthalate as a function of the concentration of areactive (additive) carrier at various molecular weights.

DETAILED DESCRIPTION

In one aspect, the invention is a polyester resin that is capable ofbeing formed into low-haze, high-clarity bottles possessing reducedcoefficient of friction. The bottle resin is characterized by theinclusion of between about 20 and 200 ppm of an inert particulateadditive, preferably either talc (i.e., a natural hydrous magnesiumsilicate of representative formula 3MgO.4SiO₂.H₂O) or precipitatedcalcium carbonate, having an average particle size of less than aboutten microns, more preferably less than two microns. The inertparticulate additive, which is preferably surface-treated, is present inlow concentrations to ensure that bottles formed from the polyesterbottle resin possess low haziness. Such improved frictionalcharacteristics reduce, and can eliminate, the need to apply, duringfilling operation, external lubricants to the surfaces of containersformed from the present polyester resin.

Preferably, the polyester resin includes between about 40 and 150 ppm ofthe inert particulate additive, more preferably between about 40 and 100ppm of the inert particulate additive, and most preferably between about60 and 100 ppm of the inert particulate additive.

In another aspect, the invention is a method for making a polyesterresin that can be formed into high-clarity bottles possessing reducedcoefficient of friction. The method generally includes reacting aterephthalate component and a diol component to form polyethyleneterephthalate precursors, e.g., bis(2-hydroxyethyl)terephthalate, whichare then polymerized via melt phase polycondensation to form polymers ofpolyethylene terephthalate of a desired molecular weight. Duringpolycondensation, which is usually enhanced by catalysts, ethyleneglycol is continuously removed to create favorable reaction kinetics.The method is characterized by the introduction of between about 20 and200 ppm of an inert particulate additive-more preferably talc or calciumcarbonate in the aforementioned concentration ranges-that is capable ofreducing the coefficient of friction in bottles formed from thepolyethylene terephthalate polymers. As noted, the friction-reducingadditive has an average particle size of less than about ten microns andis preferably either surface-modified talc or surface-modified calciumcarbonate.

Without being bound to a particular theory, it is believed that theintroduction of fillers can create discontinuous phases within thepolyethylene terephthalate resin. During stretch-blow molding, suchdiscontinuities lead to the formation of microvoids around the fillerparticles. This causes bottle haze because of differences in refractiveindex between the microvoid regions and the polyethylene terephthalatematrix. The microvoids are apparently caused by an inherentincompatibility of the filler particles with the polyethyleneterephthalate matrix.

According to the present invention, to improve compatibility between thepolyethylene terephthalate polymers and the inert particulate additive,the inert particulate additive is preferably treated with a couplingagent before its addition to polyethylene terephthalate polymers. Thishas been found to significantly reduce bottle haze while reducing bottleCOF. Without coupling agent treatment, the polyethylene terephthalatepolymers resist wetting of the inert particles. Thus, all things beingequal, surface treatment reduces polyester bottle haze.

Accordingly, the inert particulate additive is preferablysurface-modified talc or surface-modified calcium carbonate. Inparticular, talc is preferably surface treated using silanes, especiallyorganosilanes such as 3-aminopropyl trimethoxy silane and 3-aminopropyltriethoxy silane, at a loading of between about 0.5 and one weightpercent. Calcium carbonate is preferably surface treated using stearicacid at a loading of between about one and two weight percent. Treatmentwith these coupling agents (e.g., organosilane and stearic acid)facilitates compatibility between the inert particles and thepolyethylene terephthalate polymer by introducing covalent chemicalbonding between the particle surface and the polyethylene terephthalatepolymer, or by introducing a hydrophobic moiety that is compatible withthe polyethylene terephthalate to facilitate better polymer wetting ofthe particle.

The inclusion of an inert particulate additive in the polyethyleneterephthalate resin reduces bottle friction, but also increases bottlehaze. FIG. 1 depicts the trade-off between reduced friction and haze. Inbrief, concentrations of talc or calcium carbonate greater than about200 ppm (and in some instances even 100 ppm) will result in unacceptablehazy bottles, and concentrations of talc or calcium carbonate much lessthan about 20 ppm will not noticeably reduce bottle COF. As describedpreviously, the polyester resin preferably includes between about 40 and150 ppm of the inert particulate additive and most preferably betweenabout 60 and 100 ppm of the inert particulate additive.

The efficacy of the present invention is demonstrated by testing thatshows the addition of 100 ppm of surface-treated talc reducescoefficient of friction by about 90 percent, as measured using ASTM Testmethod D 1894.

Note that at any given weight fraction of inert particulate additive,increasing particle size will exacerbate haziness with no concomitantreduction in friction. An average particle size of much more than tenmicrons generally causes unacceptable bottle haze. As will be understoodby those familiar with this art, particle size is typically measured bytechniques based on light scattering. Particle sizes and distributionsare often characterized using a Hegman Fineness number determined fromASTM D1210-79.

As used herein, the term “diol component” refers primarily to ethyleneglycol, although other diols (e.g., polyethylene glycol) may be used aswell. It will be understood by those of ordinary skill in the art thatthe diol component usually forms the majority of terminal ends of thepolymer chains and so is present in the composition in slightly greaterfractions. For example, the molar ratio of the terephthalate componentand the diol component is typically between about 1.0:1.0 and 1.0:1.6.

As used herein, the term “terephthalate component” refers to diacids anddiesters that can be used to prepare polyethylene terephthalate. Inparticular, the terephthalate component mostly includes terephthalicacid and dimethyl terephthalate, but can include diacid and diestercomonomers as well. In this regard, those having ordinary skill in theart will know that there are two conventional methods for formingpolyethylene terephthalate. These methods are well known to thoseskilled in the art.

One method employs a direct esterification reaction using terephthalicacid and excess ethylene glycol. In this technique, the aforementionedstep of reacting a terephthalate component and a diol component includesreacting terephthalic acid and ethylene glycol in a heatedesterification reaction to form monomers and oligomers of terephthalicacid and ethylene glycol, as well as a water byproduct. To enable theesterification reaction to go essentially to completion, the water mustbe continuously removed as it is formed.

The other method involves a two-step ester exchange reaction andpolymerization using dimethyl terephthalate and excess ethylene glycol.In this technique, the aforementioned step of reacting a terephthalatecomponent and a diol component includes reacting dimethyl terephthalateand ethylene glycol in a heated ester exchange reaction to form monomersand oligomers of terephthalate and ethylene glycol, as well as methanolas a byproduct. To enable the ester exchange reaction to go essentiallyto completion, the methanol must be continuously removed as it isformed.

It will be understood by those having ordinary skill in the art that thepolyethylene terephthalate herein described may be a modifiedpolyethylene terephthalate to the extent the diol component can includeother glycols besides ethylene glycol (e.g., diethylene glycol,1,3-propanediol, 1,4-butanediol and 1,4-cyclohexane dimethanol), or theterephthalate component includes modififers such as isophthalic acid,2,6-naphthalene dicarboxylic acid, succinic acid, or one or morefunctional derivatives of terephthalic acid. In fact, most commercialpolyethylene terephthalate polymers are modified polyethyleneterephthalate polyesters.

An advantage of the present invention is that the inert particulateadditives may be added to any polyester bottle resin formulation toreduce COF in bottles made therefrom. In this regard, bottle gradepolyester resins will not be discussed herein in detail as such resinsare well known in the art. For example, commonly-assigned, copendingapplication Ser. No. 09/456,253 filed Dec. 7, 1999, for a Method ofPreparing Modified Polyester Bottle Resins, Now U.S. Pat. No. 6,284,866,which discusses several U.S. patents that disclose various modifiedpolyethylene terephthalate resins. This application is herebyincorporated entirely herein by reference.

While the present application is directed to polyester resins, it isbelieved that non-polyester resins, such as high-density polyethylene(HDPE), low-density polyethylene (LDPE), linear low-density polyethylene(LLDPE), polyvinyl chloride (PVC), and polyvinyl dichloride (PVDC),which are typically used in films, show analogous frictionalcharacteristics and thus benefit from the use of inert particulateadditives to reduce COF.

In the present invention, the direct esterification reaction ispreferred over the older, two-step ester exchange reaction. As noted,the direct esterification technique reacts terephthalic acid andethylene glycol to form low molecular weight monomers, oligomers, andwater.

For example, in a typical, exemplary process the continuous feed entersa direct esterification vessel that is operated at a temperature ofbetween about 240° C. and 290° C. and at a pressure of between about 5and 85 psia for between about one and five hours. The reaction, which istypically uncatalyzed, forms low molecular weight monomers, oligomers,and water. The water is removed as the esterification reaction proceedsto drive a favorable reaction equilibrium.

Thereafter, the low molecular weight monomers and oligomers arepolymerized via polycondensation to form polyethylene terephthalatepolyester. This polycondensation stage generally employs a series of twoor more vessels and is operated at a temperature of between about 250°C. and 305° C. for between about one and four hours. Thepolycondensation reaction usually begins in a first vessel called thelow polymerizer. The low polymerizer is operated at a pressure range ofbetween about 0 and 70 torr. The monomers and oligomers polycondense toform polyethylene terephthalate and ethylene glycol.

The ethylene glycol is removed from the polymer melt using an appliedvacuum to drive the reaction to completion. In this regard, the polymermelt is typically agitated to promote the escape of the ethylene glycolfrom the polymer melt and to assist the highly viscous polymer melt inmoving through the polymerization vessel.

As the polymer melt is fed into successive vessels, the molecular weightand thus the intrinsic viscosity of the polymer melt increases. Thetemperature of each vessel is generally increased and the pressuredecreased to allow greater polymerization in each successive vessel.

The final vessel, generally called the “high polymerizer,” is operatedat a pressure of between about 0 and 40 torr. Like the low polymerizer,each of the polymerization vessels is connected to a flash vessel andeach is typically agitated to facilitate the removal of ethylene glycol.The residence time in the polymerization vessels and the feed rate ofthe ethylene glycol and terephthalic acid into the continuous process isdetermined in part based on the target molecular weight of thepolyethylene terephthalate polyester. Because the molecular weight canbe readily determined based on the intrinsic viscosity of the polymermelt, the intrinsic viscosity of the polymer melt is generally used todetermine the feed rate of the reactants and the residence time withinthe polymerization vessels.

Note that in addition to the formation of polyethylene terephthalatepolymers, side reactions occur that produce undesirable by-products. Forexample, the esterification of ethylene glycol forms diethylene glycol(DEG), which is incorporated into the polymer chain. As is known tothose of skill in the art, diethylene glycol lowers the softening pointof the polymer. Moreover, cyclic oligomers (e.g., trimer and tetramersof terephthalic acid and ethylene glycol) may occur in minor amounts.The continued removal of ethylene glycol as it forms in thepolycondensation reaction will generally reduce the formation of theseby-products.

After the polymer melt exits the polycondensation stage, typically fromthe high polymerizer, it is generally filtered and extruded, preferablyimmediately after exiting the polycondensation stage. After extrusion,the polyethylene terephthalate is quenched, preferably by spraying withwater, to solidify it. The solidified polyethylene terephthalatepolyester is cut into chips or pellets for storage and handlingpurposes. As used herein, the term “pellets” is used generally to referto chips, pellets, and the like.

As will be known to those of skill in the art, the pellets formed fromthe polyethylene terephthalate polymers may be subjected tocrystallization followed by solid state polymerization (SSP) to increasethe molecular weight of the polyethylene terephthalate resin. It shouldbe noted that the method of the invention does not adversely affect theSSP rate and often will even increase the SSP rate. The polyester chipsare then re-melted and re-extruded to form bottle preforms, which canthereafter be formed into polyester containers (e.g., beverage bottles).The levels of inert particulate additives (i.e., less than 200 ppm) donot detrimentally affect cycle times during injection moldingoperations.

Although the prior discussion assumes a continuous production process,it will be understood that the invention is not so limited. Theteachings disclosed herein may be applied to semi-continuous processesand even batch processes.

The inert particulate additives herein disclosed can be introduced tothe polyethylene terephthalate polymers as a powder, as a concentrate inpolyethylene terephthalate, or as a concentrate in a liquid carrier. Thepreferred point of addition in the polyethylene terephthalatepolymerization process is after completion of polycondensation (i.e.,mixed with the molten polymer stream after the final polymerizationvessel).

In one embodiment, the method introduces an essentially dry, inertparticulate additive into the polyethylene terephthalate polymers duringor after the polycondensation stage. Dry, inert particulate additive maybe introduced via a split-stream method, such as that disclosed by U.S.Pat. No. 5,376,702 for a Process and Apparatus for the Direct andContinuous Modification of Polymer Melts. This patent discloses dividinga polymer melt stream into an unmodified stream and a branch stream thatreceives additives. In particular, a side stream takes a portion of thebranch stream to an extruder, where additives are introduced.Unfortunately, this kind of technique is not only complicated, but alsocostly, requiring at least a screw extruder and additional melt pipingto process additives. Consequently, such arrangements are inconvenientand even impractical where total additive concentrations are low (e.g.,less than one weight percent).

Most preferably, the inert particulate additives are added after themelt polymerization is complete. Such late addition is desirable becauseesterification and polycondensation conditions can cause a calciumcarbonate additive to dissolve in the polymer, which destroys itsparticulate nature. Consequently, calcium carbonate is preferably addedto the polyethylene terephthalate polymer before extrusion andpelletization.

Similarly, high polycondensation temperatures can strip coupling agents(e.g., silane surface treatment) from talc. As talc is not susceptibleto dissolution in the polymer, its addition is more adaptable than isthe addition of calcium carbonate (i.e., talc itself can be added at anypoint during the polymerization).

Accordingly, in a preferred embodiment, the method introduces the inertparticulate additive via a reactive carrier, rather than via an inertcarrier or no carrier at all. The reactive carrier, which preferably hasa molecular weight of less than about 10,000 g/mol may be introducedduring polycondensation or more preferably, after the polycondensationis complete. In either respect, the reactive carrier should beintroduced to the polyethylene terephthalate polymers in quantities suchthat bulk polymer properties are not significantly affected.

Most preferably, the reactive carrier has a melting point that ensuresthat it is a liquid or slurry at near ambient temperatures. Near ambienttemperatures not only simplify the unit operations (e.g., extruders,heaters, and piping), but also minimize degradation of the inertparticulate additives. As used herein, the term “near ambient” includestemperatures between about 20° C. and 60° C.

As a general matter, the reactive carrier should make up no more thanabout one weight percent of the polyethylene terephthalate resin.Preferably, the reactive carrier is introduced to the polyethyleneterephthalate polymers in quantities such that its concentration in thepolymer resin is less than about 1000 ppm (i.e., 0.1 weight percent).Reducing the reactive carrier to quantities such that its concentrationin the polymer resin is less than 500 ppm (i.e., 0.05 weight percent)will further reduce potential adverse effects to bulk polymerproperties.

In general, reactive carriers having carboxyl, hydroxyl, or aminefunctional groups are favored. Preferred are polyols, especiallypolyester polyols and polyether polyols, having a molecular weight thatis sufficiently high such that the polyol will not substantially reducethe intrinsic viscosity of the polyethylene terephthalate polymer, and aviscosity that facilitates pumping of the polyol. Polyethylene glycol isa preferred polyol. Other exemplary polyols include functionalpolyethers, such as polypropylene glycol that is prepared from propyleneoxide, random and block copolymers of ethylene oxide and propyleneoxide, and polytetramethylene glycol that is derived from thepolymerization of tetrahydrofuran.

Alternatively, the reactive carrier may include dimer or trimer acidsand anhydrides. In another embodiment, the reactive carrier may possess,in addition to or in place of terminal functional groups, internalfunctional groups (e.g., esters, amides, and anhydrides) that react withthe polyethylene terephthalate polymers. In yet another embodiment, thereactive carrier may include non-functional esters, amides, oranhydrides that is capable of reacting into the polyethyleneterephthalate polymers during solid state polymerization and that willnot cause the polyethylene terephthalate polymers to suffer intrinsicviscosity loss during injection molding processes.

In view of the foregoing, a preferred embodiment of the inventionincludes reacting terephthalic acid and ethylene glycol in a heatedesterification reaction to form monomers and oligomers of terephthalicacid and ethylene glycol, then polymerizing these monomers and oligomersvia melt phase polycondensation to form polyethylene terephthalatepolymers. Thereafter, between about 20 and 200 ppm of eithersurface-modified talc or surface-modified calcium carbonate isintroduced into the polyethylene terephthalate polymers using a reactivecarrier, which facilitates uniform blending within the polymer melt.Preferably, the reactive carrier is a polyol (e.g., polyethylene glycol)having a molecular weight that permits the polyol to be pumped at nearambient temperatures (e.g., less than 60° C.) and that is introduced tothe polyethylene terephthalate polymers in quantities such that bulkproperties of the polyethylene terephthalate polymers are notsignificantly affected. The polyethylene terephthalate polymers are thenformed into chips (or pellets via a polymer cutter) before being solidstate polymerized. Importantly, the polyol reactive carrier combineswith the polyethylene terephthalate polymer such that it isnon-extractable during subsequent processing operations (e.g., formingpolyester preforms or beverage containers).

As will be understood by those of ordinary skill in the art,macromolecules are considered to be polymers at an intrinsic viscosityof about 0.45 dl/g. This roughly translates to a molecular weight of atleast about 13,000 g/mol. In contrast, the reactive carriers accordingto the present invention have molecular weights that are less than about10,000 g/mol. The molecular weight of the reactive carrier is typicallyless than 6000 g/mol, preferably less than 4000 g/mol, more preferablybetween about 300 and 2000 g/mol, and most preferably between about 400and 1000 g/mol. As used herein, molecular weight refers tonumber-average molecular weight, rather than weight-average molecularweight.

FIGS. 2 and 3 illustrate the theoretical loss of intrinsic viscosity asa function of reactive carrier concentration at several molecularweights. FIG. 2 depicts the impact of the reactive carrier on uponpolyethylene terephthalate having an intrinsic viscosity of 0.63 dl/g.Similarly, FIG. 3 depicts the impact of the reactive carrier on uponpolyethylene terephthalate having intrinsic viscosity of 0.45 dl/g. Notethat at any concentration, the reactive carriers having higher molecularweights have less adverse effect upon intrinsic viscosity of the polymerresin.

As used herein, the term “intrinsic viscosity” is the ratio of thespecific viscosity of a polymer solution of known concentration to theconcentration of solute, extrapolated to zero concentration. Intrinsicviscosity, which is widely recognized as standard measurements ofpolymer characteristics, is directly proportional to average polymermolecular weight. See, e.g., Dictionary of Fiber and Textile Technology,Hoechst Celanese Corporation (1990); Tortora & Merkel, Fairchild'sDictionary of Textiles (7^(th) Edition 1996).

Intrinsic viscosity can be measured and determined without undueexperimentation by those of ordinary skill in this art. For theintrinsic viscosity values described herein, the intrinsic viscosity isdetermined by dissolving the copolyester in orthochlorophenol (OCP),measuring the relative viscosity of the solution using a SchottAutoviscometer (AVS Schott and AVS 500 Viscosystem), and thencalculating the intrinsic viscosity based on the relative viscosity.See, e.g., Dictionary of Fiber and Textile Technology (“intrinsicviscosity”).

In particular, a 0.6-gram sample (+/−0.005 g) of dried polymer sample isdissolved in about 50 ml (61.0-63.5 grams) of orthochlorophenol at atemperature of about 105° C. Fiber and yarn samples are typically cutinto small pieces, whereas chip samples are ground. After cooling toroom temperature, the solution is placed in the viscometer and therelative viscosity is measured. As noted, intrinsic viscosity iscalculated from relative viscosity.

Finally, as is understood by those familiar with polyester packaging,ultraviolet (UV) radiation absorbers protect polymers and the contentsof packages formed from the same. Where UV absorbers are added to thebottle resin during the injection molding process, there is a tendencyfor such UV absorbers (and when used, reactive carriers that deliver UVabsorbers) to leave deposits in the injection molds used for preforms.Such deposits cause the preforms to stick in the injection moldsslightly longer, thereby slowing preform manufacturing efficiency.

Without being bound to any particular theory, it is believed that theinteraction between a UV absorber and the bottle resin producesbyproducts that in turn deposit on the molds in which polyester bottlepreforms are manufactured. These deposits cause the preforms to stick inthe mold, thereby slowing the production rate of the preform-makingprocess. Calcium carbonate, and especially talc, have been found to havethe beneficial effect of reducing adherence to preform molds, therebyincreasing the speed and efficiency of the injection molding process.Accordingly, an embodiment of the polyester resin includes both an inertparticulate additive as herein described and a UV absorber.

In the drawings and the specification, typical embodiments of theinvention have been disclosed. Specific terms have been used only in ageneric and descriptive sense, and not for purposes of limitation. Thescope of the invention is set forth in the following claims.

What is claimed is:
 1. A polyester resin that is capable of being formedinto high-clarity bottles possessing reduced coefficient of friction,the resin comprising polyethylene terephthalate and between about 20 and200 ppm of an inert particulate additive selected from the groupconsisting of talc and calcium carbonate, the inert particulate additivehaving an average particle size of less than about ten microns.
 2. Apolyester resin according to claim 1, comprising between about 40 and150 ppm of the inert particulate additive.
 3. A polyester resinaccording to claim 1, comprising between about 60 and 100 ppm of theinert particulate additive.
 4. A polyester resin according to claim 1,wherein the inert particulate additive has an average particle size ofless than about two microns.
 5. A polyester resin according to claim 1,wherein the inert particulate additive is surface-modified talc.
 6. Apolyester resin according to claim 5, wherein the surface-modified talcis talc treated with an organosilane coupling agent.
 7. A polyesterresin according to claim 1, wherein the inert particulate additive issurface-modified calcium carbonate.
 8. A polyester resin according toclaim 7, wherein the surface-modified calcium carbonate is calciumcarbonate treated with a stearic acid coupling agent.
 9. A polyesterpreform made from the polyester resin of claim
 1. 10. A polyestercontainer made from the polyester resin of claim
 1. 11. A polyesterresin that is capable of being formed into high-clarity bottlespossessing reduced coefficient of friction, the resin comprisingpolyethylene terephthalate and between about 40 and 100 ppm of an inertparticulate additive selected from the group consisting ofsurface-modified talc and surface-modified calcium carbonate, the inertparticulate additive having an average particle size of less than abouttwo microns.
 12. A polyester resin that is capable of being formed intohigh-clarity bottles possessing reduced coefficient of friction, theresin comprising polyethylene terephthalate and between about 20 and 200ppm of surface-modified talc having an average particle size of lessthan about ten microns.
 13. A polyester resin according to claim 12,comprising between about 40 and 150 ppm of the inert particulateadditive.
 14. A polyester resin according to claim 12, comprisingbetween about 60 and 100 ppm of the inert particulate additive.
 15. Apreform made from the polyester resin of claim
 12. 16. A container madefrom the polyester resin of claim 12, the container having high clarityand possessing a reduced coefficient of friction.
 17. A polyester resinaccording to claim 12, wherein the inert particulate additive has anaverage particle size of less than about two microns.
 18. A polyesterresin according to claim 17, comprising between about 40 and 150 ppm ofthe inert particulate additive.
 19. A polyester resin according to claim17, comprising between about 60 and 100 ppm of the inert particulateadditive.
 20. A preform or container made from the polyester resin ofclaim
 17. 21. A polyester resin according to claim 12, wherein thesurface-modified talc is talc treated with an organosilane couplingagent.
 22. A polyester resin according to claim 21, comprising betweenabout 40 and 150 ppm of the inert particulate additive.
 23. A polyesterresin according to claim 21, comprising between about 60 and 100 ppm ofthe inert particulate additive.
 24. A polyester resin according to claim21, wherein the inert particulate additive has an average particle sizeof less than about two microns.
 25. A preform or container made from thepolyester resin of claim
 21. 26. A polyester resin that is capable ofbeing formed into high-clarity bottles possessing reduced coefficient offriction, the resin comprising polyethylene terephthalate and betweenabout 20 and 200 ppm of surface-modified calcium carbonate having anaverage particle size of less than about ten microns.
 27. A polyesterresin according to claim 26, comprising between about 40 and 150 ppm ofthe inert particulate additive.
 28. A polyester resin according to claim26, comprising between about 60 and 100 ppm of the inert particulateadditive.
 29. A preform made from the polyester resin of claim
 26. 30. Acontainer made from the polyester resin of claim 26, the containerhaving high clarity and possessing a reduced coefficient of friction.31. A polyester resin according to claim 26, wherein the inertparticulate additive has an average particle size of less than about twomicrons.
 32. A polyester resin according to claim 31, comprising betweenabout 40 and 150 ppm of the inert particulate additive.
 33. A polyesterresin according to claim 31, comprising between about 60 and 100 ppm ofthe inert particulate additive.
 34. A preform or container made from thepolyester resin of claim
 31. 35. A polyester resin according to claim26, wherein the surface-modified calcium carbonate is calcium carbonatetreated with a stearic acid coupling agent.
 36. A polyester resinaccording to claim 35, comprising between about 40 and 150 ppm of theinert particulate additive.
 37. A polyester resin according to claim 35,comprising between about 60 and 100 ppm of the inert particulateadditive.
 38. A polyester resin according to claim 35, wherein the inertparticulate additive has an average particle size of less than about twomicrons.
 39. A preform or container made from the polyester resin ofclaim 35.